Safe Haskell | None |
---|---|
Language | Haskell2010 |
Ouroboros.Consensus.Forecast
Contents
Synopsis
-
data
Forecast
a =
Forecast
{
- forecastAt :: WithOrigin SlotNo
- forecastFor :: SlotNo -> Except OutsideForecastRange ( Ticked a)
-
data
OutsideForecastRange
=
OutsideForecastRange
{
- outsideForecastAt :: !( WithOrigin SlotNo )
- outsideForecastMaxFor :: ! SlotNo
- outsideForecastFor :: ! SlotNo
- constantForecastOf :: Ticked a -> WithOrigin SlotNo -> Forecast a
- mapForecast :: ( Ticked a -> Ticked b) -> Forecast a -> Forecast b
- trivialForecast :: GetTip b => b -> Forecast ()
- crossEraForecastBound :: WithOrigin SlotNo -> SlotNo -> Word64 -> Word64 -> SlotNo
Documentation
Forecast the effect of time ticking
Constructors
Forecast | |
Fields
|
data OutsideForecastRange Source #
Constructors
OutsideForecastRange | |
Fields
|
Instances
Eq OutsideForecastRange Source # | |
Defined in Ouroboros.Consensus.Forecast Methods (==) :: OutsideForecastRange -> OutsideForecastRange -> Bool Source # (/=) :: OutsideForecastRange -> OutsideForecastRange -> Bool Source # |
|
Show OutsideForecastRange Source # | |
Defined in Ouroboros.Consensus.Forecast |
|
Exception OutsideForecastRange Source # | |
Defined in Ouroboros.Consensus.Forecast Methods toException :: OutsideForecastRange -> SomeException Source # fromException :: SomeException -> Maybe OutsideForecastRange Source # |
constantForecastOf :: Ticked a -> WithOrigin SlotNo -> Forecast a Source #
Forecast where the values are never changing
This is primarily useful for tests; the forecast range is infinite, but we do still check the precondition, to catch any bugs.
trivialForecast :: GetTip b => b -> Forecast () Source #
Trivial forecast of values of type
()
performed by an instance of
GetTip
.
Specialization of
constantForecast
.
Utilities for constructing forecasts
crossEraForecastBound Source #
Arguments
:: WithOrigin SlotNo |
Current tip (the slot the forecast is at) |
-> SlotNo |
Slot at which the transition to the next era happens |
-> Word64 |
Max lookeahead in the current era |
-> Word64 |
Max lookeahead in the next era |
-> SlotNo |
Compute the upper bound for a range for a forecast across eras.
We have to be very careful here in how we compute the maximum lookahead. As long as we are in a single era, things look like this:
/-------------------\ | | chain ... - block - block - block [block] | | v ledger TIP VIEW
where
TIP
is the current ledger tip and
VIEW
is the last ledger view we
can forecast, because the next block
[block]
to arrive will take effect in
the next leger state after
VIEW
. Note that if the maximum lookahead is
zero, this looks like
chain ... - block - block - block [block] | | ledger TIP
where
[block]
can have immediate changes on the ledger, and so we can't
look ahead at all (of course, we always know the
current
TIP
).
Note that blocks arriving
after
[block]
can only take effect
later
than
[block]
, and so they are not relevant for computing the maximum slot number
we can compute a ledger view for.
Now, if we are near an era transition, this picture gets a bit more complicated. If the next block is still in this era (that is, unless we are right at the edge), then that imposes one constraint, as before. However, the first block in the next era imposes an additional constraint:
~ ~ /------------------\ ~ | | /---------- ~ ---|----------\ | | ~ | | | block [block] ~ [block'] | | | ~ v v TIP ~ VIEW ~
There are no restrictions on the relative values of these two maximum lookahead values. This means that it's quite possible for the next era to have a smaller lookahead (to re-iterate, since that era has not yet begun, the first block in that era is at the transition, and so the maximum lookahead applies from the transition point):
~ ~ /----------\ ~ | | /---------- ~ ---|----------|-------\ | ~ | | | block [block] ~ [block'] | | | ~ v v TIP ~ VIEW ~
Indeed, if the next era has zero lookahead, when the first block of the next era comes it, it can make changes immediately, and so we can't even know what the view at the transition point is.
Note that if there can be no more blocks in this era, the maximum lookahead of the current era is irrelevant:
~ ~ /----------\ ~ | | ~ | | ~ | | block ~ [block'] | | ~ v TIP ~ VIEW ~
We can therefore compute the earliest
SlotNo
the next block in this era
(if any) can make changes to the ledger state, as well as the earliest
SlotNo
the first block in the next era can; their
minimum
will serve as
an exclusive upper bound for the forecast range.